The stopping behaviour of baryons in massive heavy ion collisions ( s k 10AGeV) is investigated within di erent microscopic models. At SPS-energies the predictions range from full stopping to virtually total transparency. Experimental data are indicating strong stopping. The initial baryo-chemical potentials and temperatures at collider energies and their impact on the formation probability of strange baryon clusters and strangelets are discussed.

We demonstrate the occurrence of canonical suppression associated with the conservation of an U(1)-charge in current transport models. For this study a pion gas is simulated within two different transport approaches by incorporating inelastic and volume-limited collisions pi pi leftrightarrow K bar-K for the production of kaon pairs. Both descriptions can dynamically account for the suppression in the yields of rare strange particles in a limited box, being in full accordance with a canonical statistical description.

A scenario of heavy resonances, called massive Hagedorn states, is proposed which exhibits a fast (t H 1 fm/c) chemical equilibration of (strange) baryons and anti-baryons at the QCD critical temperature Tc. For relativistic heavy ion collisions this scenario predicts that hadronization is followed by a brief expansion phase during which the equilibration rate is higher than the expansion rate, so that baryons and antibaryons reach chemical equilibrium before chemical freeze-out occurs. PACS-Nr.: 12.38.Mh

Fast thermalization and a strong build up of elliptic flow of QCD matter were investigated within the pQCD based 3+1 dimensional parton transport model BAMPS including bremsstrahlung 2 <-> 3 processes. Within the same framework quenching of gluonic jets in Au+Au collisions at RHIC can be understood. The development of conical structure by gluonic jets is investigated in a static box for the regimes of small and large dissipation. Furthermore we demonstrate two different approaches to extract the shear viscosity coefficient n from a microscopical picture.

We demonstrate that the creation of strange matter is conceivable in the midrapidity region of heavy ion collisions at Brookhaven RHIC and CERN LHC. A finite net-baryon density, abundant (anti)strangeness production, as well as strong net-baryon and net-strangeness fluctuations, provide suitable initial conditions for the formation of strangelets or metastable exotic multistrange ( baryonic) objects. Even at very high initial entropy per baryon SyAinit ¯ 500 and low initial baryon numbers of Ainit B ¯ 30 a quark-gluon-plasma droplet can immediately charge up with strangeness and accumulate net-baryon number. PACS numbers: 25.75.Dw, 12.38.Mh, 24.85.+

We demonstrate that strangeness separates in the Gibbs-phase coexistence between a baryon-rich quark-gluon plasma and hadron matter, even at T=0. For finite temperatures this is due to the associated production of kaons (containing s¯ quarks) in the hadron phase while s quarks remain in the deconfined phase. The s-s¯ separation results in a strong enhancement of the s-quark abundance in the quark phase. This mechanism is further supported by cooling and net strangeness enrichment due to the prefreezeout evaporation of pions and K+, K0, which carry away entropy and anti- strangeness from the system. Metastable droplets (i.e., stable as far as weak interactions are not regarded) of strange-quark matter (‘‘strangelets’’) can thus be formed during the phase transition. Such cool, compact, long-lived clusters could be experimentally observed by their unusually small Z/A ratio (&#8804;0.1–0.3). Even if the strange-quark-matter phase is not stable under strong interactions, it should be observable by the delayed correlated emission of several hyperons. This would serve as a unique signature for the transient formation of a quark-gluon plasma.

We discuss the properties of two distinct forms of hypothetical strange matter, small lumps of strange quark matter (strangelets) and of hyperon matter (metastable exotic multihypernuclear objects: MEMOs), with special empha- sis on their relevance for present and future heavy ion experiments. The masses of small strangelets up to AB = 40 are calculated using the MIT bag model with shell mode filling for various bag parameters. The strangelets are checked for possible strong and weak hadronic decays, also taking into account multiple hadron decays. It is found that strangelets which are stable against strong decay are most likely highly negative charged, contrary to previous findings. Strangelets can be stable against weak hadronic decay but their masses and charges are still rather high. This has serious impact on the present high sensitivity searches in heavy ion experiments at the AGS and CERN facilities. On the other hand, highly charged MEMOs are predicted on the basis of an extended relativistic mean field model. Those objects could be detected in future experiments searching for short lived, rare composites. It is demonstrated that future experiments can be sensitive to a much wider variety of strangelets.

Second-order dissipative hydrodynamic equations for each component of a multi-component system are derived using the entropy principle. Comparison of the solutions with kinetic transport results demonstrates validity of the obtained equations. We demonstrate how the shear viscosity of the total system can be calculated in terms of the involved cross-sections and partial densities. The presence of the inter-species interactions leads to a characteristic time dependence of the shear viscosity of the mixture, which also means that the shear viscosity of a mixture cannot be calculated using the Green-Kubo formalism the way it has been done recently. This finding is of interest for understanding of the shear viscosity of a quark-gluon plasma extracted from comparisons of hydrodynamic simulations with experimental results from RHIC and LHC.

Recently it has been suggested that rather cold droplets of absolutely stable or metastable strange-quark matter may be distilled in heavy-ion collisions during the phase transition from a baryon-rich quark-gluon plasma (QGP) to hadron matter. Here we present a model describing the hadronization of the QGP through particle emission, which is based solely on thermodynamical arguments. Pions and K+’s and K0’s carry away entropy and antistrangeness from the system, thus facilitating the cooling process and the strangelet formation. Our results are supported by revised more sophisticated rate calculations. Two rather unexpected results are obtained when this model is applied to the investigation of strangelet production. The strangeness separation mechanism and the formation process works well even for higher initial entropies per baryon, tantamount to higher bombarding energies. The surviving strangelets have a rather high strangeness content, fs&#8764;1.2–2 [i.e., Z/A&#8764;(-0.1)–(-0.5)]. Hence droplets of strange-quark matter with a baryon number of &#8764;10–30 and with a negative charge may be produced. They may serve as a unique signature for the transient formation of a quark-gluon plasma in heavy-ion collisions.

We calculate the evolution of quark-gluon-plasma droplets during the hadronization in a thermodynamical model. It is speculated that cooling as well as strangeness enrichment allow for the formation of strangelets even at very high initial entropy per baryon S/Ainit H 500 and low initial baryon numbers of Ainit B H 30. It is shown that the droplet with vanishing initial chemical potential of strange quarks and a very moderate chemical potential of up/down quarks immediately charges up with strangeness. Baryon densi- ties of H 2 0 and strange chemical potentials of µs > 350 MeV are reached if strangelets are stable. The importance of net baryon and net strangeness fluctuations for the possible strangelet formation at RHIC and LHC is em- phasized. Pacs-Classif.: 25.15.tr, 12.38.Mh, 24.85.tp